1. Field of the Invention
This invention relates to a new process for the production of uretdione group-containing polyisocyanates by the partial dimerization of the isocyanate groups of organic diisocyanates with aliphatically- and/or cycloaliphatically-bound isocyanate groups using antimony(V)fluoride as the dimerization catalyst.
2. Description of the Prior Art
Processes for the production of uretdiones by the dimerization of aliphatic isocyanates are known. According to DE-OS No. 1,670,720, phosphines or boron trifluoride are used as dimerization catalysts. These catalysts suffer from the disadvantage that substantial quantities of isocyanurates are formed as by-products during the dimerization reaction. According to DE-OS No. 3,227,779, certain amino-phosphines, for example tri-(dimethylamino)-phosphine, are used as dimerization catalysts for the dimerization of certain starting diisocyanates such as diisocyanatohexanes having a branched carbon chain. These aminophosphines, according to this prior publication, permit the dimerization of the particular starting diisocyanates with a substantially improved yield of uretdione groups. The production of uretdione group-containing polyisocyanates, based on other aliphatic or cycloaliphatic diisocyanates than the particular compounds mentioned above, is not disclosed in this prior publication.
Thus, an object of the present invention is to provide a new process permitting the dimerization of any organic diisocyanates having aliphatically- and/or cycloaliphatically-bound isocyanate groups in high yields without the formation of undesirable by-products.
This object may be achieved by the present process which will be described in more detail in the following.